The present invention relates to a composting device for night soil and other biodegradable material, comprising a receptacle for receiving the material to be composted and on the bottom of which a starting bed is to be spread out, which receptacle comprises an inner, seal-tight lining in the form of a sack made from a flexible, liquid-impermeable material and a carrier intended to support the sack, the sack being constructed with liquid drains for the drainage of liquid which is separated from the composting material.
Composting devices of the above-specified type represent, from an environmental viewpoint, a substantially better alternative for the handling of biodegradable material than the water-rinsing systems frequently used at present, which result in serious and accelerating environmental destruction and high wastage of drinking water, which is one of our most vital natural resources. A more detailed description of the decomposition process which is employed is not included here, since this is well documented in earlier patent specifications.
In order for composting devices of this type, which, apart from night soil, can also manage other degradable domestic waste, to acquire a wider practical use, the devices are required to be simple to operate, adaptable to different requirements and preconditions and should allow simple rectification of operating breakdowns, for example following sabotage or misuse.
In my earlier Swedish patent application 9504794-9, a composting device is described in which the decomposition of the material takes place in a fixed receptacle, formed compost earth being removed through a lower hatch. This device works well in many cases but is open to improvement in certain regards. This applies, inter alia, to the raking-out of the compost earth, which is effected by opening the hatch and raking the earth out into an open vessel. This can be rather unpleasant, especially where the receptacle is placed in a living area or the like.
Following sabotage or misuse, for example, in which, for example, an agent intended for a chemical toilet has been poured down into the compost, thereby bringing an end to the decomposition process, removing and replacing the compost bed with a new starting bed is a time-consuming and disagreeable task, since the freshly delivered material has to be raked out into an open vessel. Corresponding problems can arise in connection with temporary overloading of a toilet installation, which results in the receptacle having to be emptied before the material has managed to decompose. This problem also arises in the temporary use of composting devices of this type in, for example, refugee camps or at other sites where large numbers of people are gathered for an indefinite period. When such a camp is to be broken up, the composting receptacles also contain fresh night soil, which has to be managed. Here there may also be risks of spreading of pathogenic bacteria. In order to kill such bacteria, a composting period of about 2 years is required.
The use of toilet installations having fixed receptacles also gives rise, in another context, to problems resulting from the limited capacity, since, when overloaded, they have to be shut off to allow the natural process to catch up, which means that the entire toilet must be kept shut during the recovery period. This is a serious limitation in connection with public installations, since it is costly to set up reserve toilets.
Certain previously used receptacles are provided with a tank which is openly connected to a receptacle. In these, leakage risks are also present in connection with overfilling of liquid in the receptacle.
GB-A-2087860 describes a device for producing liquid fertilizer from, above all, garden waste. The device does not therefore constitute a composting device of the type to which the invention relates, in which a starting bed is prepared in the receptacle and compostable material is then successively delivered over a lengthy period as previously delivered material continues to be broken down. In the previously known device for obtaining fertilizer, a sack is filled full of garden waste in one operation, after which liquid formed is collected. In addition, the flexible sack is constructed with a perforated bottom, which means that it cannot be sealed without liquid always being able to escape through the perforations.
A main object of the present invention is to achieve a cheap and simple composing device which solves, inter alia, the aforementioned problems regarding the management of compost earth and composting material in the course of decomposition, as well as the problem with the limited capacity of toilet installations having fixed receptacles.
The basis for the invention is the realization that the solid material left in a composting toilet after separation of the liquid is reduced by 95-98% in terms of volume during the composting. This means that the compost earth formed can be collected in a receptacle over a long period. The receptacle may then be emptied of all material, including both compost earth and fresh composting material that has been delivered.
According to the invention, the composting must in this case take place in a sack made from liquid-impermeable material, which only needs to be changed at long time intervals and can also be used for the maturing of fresh material for a further 1 to 2 years at a suitable site, if required.
The invention is therefore based on a concept different from that of the previously known inventions. In these, the composting is effected in a fixed receptacle and compost earth is raked out as and when it is formed. According to the invention, the composting takes place in a closed sack which is changed once it is full. It contains in this case both compost earth and non-fully decomposed material and is therefore left to mature at a suitable site.
What is especially characteristic of a composting device of the type indicated in the introduction is, according to the present invention, that the carrier and the sack-lined receptacle are arranged such that they can be transported as a unit to a depot after the sack has been wholly or partially filled, and that the bottom of the carrier is constructed with openable hatches, which allow the sack with its contents to be deposited in the depot through the said bottom when the carrier is lifted.
The fact that the composting takes place in a sack enables all the composting material, both old and fresh, to be easily removed should this be required, for example as a result of the decomposition process having come to a halt. After this, a new sack is inserted, containing a working compost bed. All handling of the composting material up to its total decay will be conducted in a closed but aerated sack, which, inter alia, prevents spreading of pathogenic bacteria. The closed sack can additionally be handled without inconvenience, including in furnished rooms. Nor is there any risk of liquid leakage during transportation and storage of the sack.
Should overloading occur, furthermore, a full sack can be removed directly and transported to a depot for maturing and be replaced by a new sack with compost bed. Alternatively, the receptacle containing the full sack can be put aside for a while and subsequently reinserted once the volume has been reduced due to the ongoing decomposition process.
In order to facilitate the depositing of the sack, in a preferred embodiment the carrier is constructed with bottom hatches, which can be op ened by being swung downwards in order to free the sack as the carrier is lifted. The sack can thus be deposited on the ground without having needed to be handled without support.
The sack expediently contains a screening device connected to the liquid drains of the sack. In a preferred embodiment, the screening device has the form of a perforated pipe extending over the bottom of the sack.
Since the seal of the composting receptacle is formed by the sack, the receptacle can otherwise have a simple construction allowing it to be mounted on the spot, which, inter alia, means that freight and storage costs can be minimized. The wall sections can in this case comprise simple panels made from cheap material.
The fact that the wall of the sack is supported by stiff wall sections and the transportation of the sack takes place whilst it is still supported by these sections and the underlying carrier, means that the sack can be made from a relatively thin and cheap plastics material, expediently a material which decomposes in nature after a few years.
The sloping plane is expediently constructed with grooves running in the direction of slope and in which liquid which is separated from the composting material is conducted to the drains of the sack. The liquid is spread over the plane, preventing all the liquid being channelled to a tunnel formed in the material.
The sloping plane is preferably situated beneath and forms a supporting surface for the sack. The plane can have the form of a separate unit, similar to a corrugated sheet, which is supported by the carrier.
In a preferred embodiment, the device comprises a lid, which fits over the wall sections mounted on the carrier. The sack can be held in place by its upper edge portion being folded over the upper edges of the wall sections and being pressed firmly against these by the lid.
The wall sections expediently have the form of stiff panels, the lower edges of which are fixed pivotably to the carrier and which, once mounted, are locked together to form a supporting shell for the sack.
The carrier is preferably constructed with two sloping planes, which can slope either towards or away from each other. A screening device is in this case disposed in the sack parallel to the lower edge of the respective sloping plane.
Other special features and characteristics of the invention are evident from the patent claims.